Third generation partnership project (3GPP) mobile communication systems based on a wideband code division multiple access (WCDMA) radio access technology are widely spread all over the world. High-speed downlink packet access (HSDPA) that can be defined as a first evolutionary stage of WCDMA provides 3GPP with a radio access technique that is highly competitive in the mid-term future. However, since requirements and expectations of users and service providers are continuously increased and developments of competing radio access techniques are continuously in progress, new technical evolutions in 3GPP are required to secure competitiveness in the future. Reduction of cost per bit, increase of service availability, flexible use of frequency bands, simple structure and open interface, proper power consumption of a user equipment (UE), and the like are defined as requirements.
An orthogonal frequency division multiplexing (OFDM) system capable of reducing inter-symbol interference with a low complexity is taken into consideration as one of post-third generation wireless communication systems. In the OFDM, a serially input data symbol is converted into N parallel data symbols, and is then transmitted by being carried on each of separated N subcarriers. The subcarriers maintain orthogonality in a frequency dimension. Each orthogonal channel experiences mutually independent frequency selective fading, and an interval of a transmitted symbol is increased, thereby minimizing inter-symbol interference.
When the UE intends to transmit uplink data, the UE requests a base station (BS) to allocate a radio resource. A method of requesting the radio resource allocation by the UE includes a scheduling request (SR), a buffer status report (BSR), a random access, etc. In general, when a radio resource is allocated to the UE by the BS within a predetermined time, uplink data can be transmitted by the allocated radio resource.
FIG. 1 is a flowchart showing an example of an uplink data transmission process.
Referring to FIG. 1, when a UE intends to transmit uplink data, the UE transmits a radio resource request message to a BS (step S100) and starts a timer (step S110). The timer is for receiving a radio resource allocation message from the BS in response to the radio resource request message.
The UE receives the radio resource allocation message from the BS before the timer expires (step S120), and transmits uplink data based on a radio resource's location and amount included in the radio resource allocation message (step S130). If the UE fails to receive the radio resource allocation message until the timer expires, the UE determines that the radio resource request has failed, and repeats the radio resource request process of step S100 and step S110.
In FIG. 1, if the timer's expiry time is set to be shorter than necessary, the UE may promptly determine that the radio resource request has failed and thus the radio resource request process may be unnecessarily repeated. Otherwise, if the timer's expiry time is set to be longer than necessary, it takes a significantly long time for the UE to determine the failure of the radio resource request, resulting in a problem of time delay.
Accordingly, there is a need for a method of properly setting the timer's expiry time so that the UE receives the radio resource allocation message of the BS in response to the radio resource request message of the UE.